WELLFLEET — Tom O'Connell and Laura Runkel live in a Cape on a lush 2 acres on Upper Pole Dike Creek with a view of the marsh and cattails stretching from their backyard to the horizon.

But they worry their freshwater paradise is at risk under the proposal to restore tidal flooding to 1,100 acres of the Herring River flood plain. And they have already said no to the first step in the $25 million to $50 million proposal that would affect their property.

The Outer Cape project is the largest salt-marsh restoration project from Maine to New York. Under the auspices of Wellfleet, Truro and the Cape Cod National Seashore, the project is now in an engineering and permitting phase that is scheduled for completion in 2016, assuming full federal funding. Construction could begin as early as 2016, with an estimated 10 years of monitoring, evaluation and adaptation to meet the project goals.

Next, Seashore officials will file a final environmental impact statement with the National Park Service, recommending how high the tides will be allowed to rise.

The Seashore owns about 80 percent of the acreage surrounding the river and its tributaries, but flooding also would affect about 375 low-lying private properties and the Chequessett Yacht & Country Club in Wellfleet. Among those, project officials have identified 20 homeowners, including Runkel and O'Connell, at greatest risk of flooding.

The four scenarios under consideration range from doing nothing to three plans with higher and higher tide levels, all of which would affect private property. The flooding would be gradual, followed by monitoring to judge the effects; then more flooding, then more monitoring, and so on.

The restoration committee and the Park Service recommended that the plan with the highest tides be accepted, but the final decision by the regional director of the park service is expected early next year.

Runkel and O'Connell would like the wetlands on Upper Pole Dike Creek excluded from the project, and declined on Aug. 8 to participate in an engineering analysis of their property for the restoration as it is planned to date.

"I know they're doing this for good reasons, but we'd like to see more balance in the process," Runkel said.

"We said, 'No,'" O'Connell said.

"We thought about it, and we said, 'No,'" Runkel added.

The Herring River originates in the northeast corner of Wellfleet at Herring Pond and then runs southwest about 4 miles to Wellfleet Harbor. Four tributaries to the river, including one from Truro, creates a wide marsh system that stretches from Route 6 west to Cape Cod Bay.

In 1909, the Chequessett Neck Road dike was constructed at the mouth of the river to drain the area and control mosquitoes. But that didn't work well enough, so in the 1930s ditches were dug upstream to further drain the area. In time, freshwater grasses, trees and shrubs and the animals they support took over the landscape.

But now, scientists say restoring the full saltwater tides will prevent fish kills, improve water quality, restore native plants and animals, and allow sediment to build up to protect the coast from rising seas, according to a draft of the environmental impact statement, unveiled last November.

The river is listed as "impaired" by the U.S. Environmental Protection Agency because of pollutants caused by the lack of tidal flushing.

In the 1980s, fish kills in the flood plain attracted the Seashore to the project. Over the next 20 years, Wellfleet, Truro and the Seashore came together to investigate whether a restoration could work and to create a plan.

Now the Herring River Restoration Committee oversees the project, meeting monthly at Seashore headquarters in South Wellfleet. Members include representatives from the Seashore, as well as other federal agencies, the state and the two towns.

The nonprofit Friends of Herring River solicits the project's grants and donations, and manages contracts for services such as engineering and staff, including part-time project coordinator Margo Fenn. The nonprofit recently was awarded a National Oceanic and Atmospheric Administration grant to spend over three years. So far, NOAA has approved spending $300,000, Don Palladino, president of the Friends board, said.

"If we have healthy wetlands, we're going to be better able as a region to withstand the climate change that we can anticipate in the next 50 or 100 years," Seashore Superintendent George Price said recently. "I also understand that there are a number of private properties. ... Those are very real concerns, and we're working with the committee to come up with a resolution."

The address list of the 375 lowest-lying properties was released publicly on Oct. 15, despite earlier requests in the last year from Runkel and the Times.

"This is a work in progress," Price said. "Giving out private addresses is not something I would not want to do either."

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O'Connell, an artist, and Runkel, a scientist, are the first private property owners to reject the project. They met with Truro Assistant Town Administrator/Planner Charleen Greenhalgh on Nov. 30 and the restoration committee June 19 to understand what they're facing, and were assured that their land isn't being taken by eminent domain.

"We asked, 'Which of your agencies has the power to flood my land?'" Runkel said. "They said, 'Oh, none of us do. We're talking about arrangements with individual property owners, to get their agreement.'"

The draft environmental impact statement doesn't say anything about saying 'no,' Runkel said.

"I responded to say we are not interested in the engineering study because we do not think this area should be included in the restoration," Runkel said. "We have heard nothing more in response to that or otherwise."

Their property, about 10 feet above sea level, is off Route 6. A steep, dirt driveway leads to their three-bedroom Cape and a yard that is at the level of the marsh. Trees and brush protect the house from the highway but rain runoff can flood the yard and seep into the garage where O'Connell stores his artwork. The thought of seeing even more water from the marsh is unthinkable, the couple said. The assessed value of their home is $336,000.

So far, because of funding limitations, only three of the 20 at-risk property owners have been asked to allow an engineering study on their property, Fenn said. Two are participating, she said.

As Runkel and O'Connell understand it, at high tide under the most extreme plan, the waters could come to the edge of their yard, near their steps, and, during a 100-year storm, be level with the floor of their house. So far, the committee has told them an earthen berm could prevent flooding on their land.

Among the five tributaries feeding into the river, Upper Pole Dike Creek, where Runkel and O'Connell live, has the largest concentration of private properties.

Given Runkel and O'Connell's negative response, one possible solution could be controlling flood levels with a tide gate for the Upper Pole Dike Creek basin, Fenn said recently. "(Options) would be limited by what we're able to work out with the property owners," she said.

The restoration of salt marshes is on the rise in New England, but "no projects really come close to the size of the Herring River project," said Maggie Mooney-Seus, a NOAA spokeswoman.

The U.S. Department of the Interior just awarded $7.5 million to restore tidal flow across 270 acres on Cape Cod, at Parkers River in South Yarmouth and Muddy River in Chatham and Harwich, in the wake of Hurricane Sandy. The Seashore fully restored tides to 400 acres of Hatches Harbor in Provincetown in 2005 and is working on a limited restoration to a 400-acre salt marsh at East Harbor, or Pilgrim Lake, in North Truro. Discussions are also underway about restoring tidal flushing to the 160-acre upper section of the Pamet River valley in Truro, which is a combination of private and public property.

For more than 20 years, John Portnoy, a Seashore staff ecologist, led efforts to restore drained and restricted salt marshes under federal control, including Hatches Harbor and East Harbor. His research, published in 1997, forms the scientific basis of the Herring River restoration, according to Department of the Interior records. Both he and Price point to existing salt marshes in Wellfleet as proof of their visual and environmental value.

"Imagine how much less attractive Wellfleet Center would be," Portnoy said, referring specifically to the Duck Creek salt marsh.

Across the marsh from Runkel and O'Connell, Abbe Seldin has learned in the last year that the creek on the back of her 1-acre lot on Coles Neck Road could become a river with the restoration project. Her four-bedroom house was built around 1995. The assessed value is $468,000.

"Most of my property falls into the area that will become wetlands," Seldin said recently. "I'm really close to it."

Seldin met one-on-one with Greenhalgh on April 16.

"She did try to answer all my concerns," Seldin said. But Seldin is still worried about whether she will have full control over her property, for example, if she will be allowed to plant whatever she chooses. She wonders whether there will be more mosquitoes and whether a big storm could flood her house.

"Eastern box turtles are all over the place," Seldin said about the freshwater marsh. "Their whole environment is going to be affected. That really bothers me, how it will affect other animals."

Given the gradual introduction of flooding, freshwater species will have time to seek out other habitat, to essentially move and adapt, Wellfleet Health and Conservation Agent Hillary Greenberg-Lemos said in response.

Runkel and O'Connell met Seldin in the last year, and they have become friends over their common worries.

Mostly, however, the Herring River project seems to be moving ahead with little opportunity for private property owners in the flood plain to compare notes with other property owners, Runkel and O'Connell said. The project committee's one-on-one approach is probably not a deliberate attempt to isolate them, Runkel said, but it has that effect.

The one-on-one approach was the committee's way of trying to give each owner attention, given that every property is unique, Greenberg-Lemos said.

"If you had a big meeting, you couldn't give them to time they would need," she said. "There's no intention to be devious. We thought that was the most beneficial way."

For Runkel and Seldin, though, the address list is about reaching out. They've created a database of the property owners and are contacting everyone to see if they would like to receive email updates.

A small group of the property owners have begun to meet as well, Runkel said.

"We don't know where people stand," Runkel said. "We're not trying to influence people's politics. It's really about information sharing."